By Dennis Collin
When working with Revit families, for MEP users there is frequently a need to be able to configure families with many different parameters which do not always relate to each other consistently. This makes controlling them with formula rather difficult. Fortunately, Revit families can utilise lookup tables to manage parameters. These tables are standard CSV (comma separated value) files which can be created in Excel, Notepad or another similar application. The files contain listings of component sizes and other numerical values and when families are altered, Revit will scan the lookup table and apply corresponding values to other parameters, in accordance with manufacturer’s product listings and saving the Revit user doing it themselves!
Lookup tables are typically found in Revit MEP families such as pipe fittings and accessories, but they can be employed with other disciplines to help control parameters on such objects like Doors, Windows and Curtain Panels.
The first column of a lookup table isn’t used by Revit and can be used as a simple remarks’ column for later reference. Second and subsequent columns require headers detailing the parameter name, the type of parameter used and the unit required, in most cases this is millimetres. Double Hash symbols are used as separators.
For textual information, the heading is different, simply type in the parameter name and set ‘other’ as the data type. It is important to remember that all textual information is contained within double quotation marks as per Fig 1.
Once created, the lookup table can be saved as a CSV file and imported into the Revit family document. Revit parameters can be set to scan the lookup table with a simple formula.
In the figure below, formulae have been applied to Inner, Outer Diameter and fitting length parameters. These formulae scan the lookup table and apply values according to the Nominal Diameter parameter which serves as an index.
The parameter ‘CADLINE_NOTES’ is a text based, instance parameter which also has a formula but scanning for an appropriate product code which corresponds with the Nominal Diameter parameter.
Setting the diameter to 80 yields a Product Code 9, but changing it to 100 alters the code to 12. This is in accordance with the data within the family’s lookup table on Fig 1.
This tip works with all Revit versions since 2019. Hopefully, this functionality will be improved upon and made easier in future versions.
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